De-regulated assimilation and over-production of amino acids in analogue-resistant mutants of a cyanobacterium, Phormidium uncinatum

1995 ◽  
Vol 11 (6) ◽  
pp. 665-668 ◽  
Author(s):  
N. S. Rao ◽  
T. M. Shakila ◽  
S. N. Bagchi
Keyword(s):  
Amino Acids ◽  
Phormidium Uncinatum ◽  
Resistant Mutants

scholarly journals Intracellular Accumulation of Mannopine, an Opine Produced by Crown Gall Tumors, Transiently Inhibits Growth of Agrobacterium tumefaciens

2001 ◽  
Vol 14 (6) ◽  
pp. 793-803 ◽  
Author(s):  
Kun-Soo Kim ◽  
Chang-Ho Baek ◽  
Jeong Kug Lee ◽  
Jai Myung Yang ◽  
Stephen K. Farrand
Keyword(s):  
Amino Acids ◽  
Agrobacterium Tumefaciens ◽  
Sole Carbon Source ◽  
Viable Cell ◽  
Insertion Mutation ◽  
Intracellular Accumulation ◽  
Cell Counts ◽  
Hexose Sugars ◽  
Crown Gall Tumors ◽  
Resistant Mutants

pYDH208, a cosmid clone from the octopine-mannityl opine-type tumor-inducing (Ti) plasmid pTi15955 confers utilization of mannopine (MOP) and agropine (AGR) on Agrobacterium tumefaciens strain NT1. NT1 harboring pYDH208 with an insertion mutation in mocC, which codes for MOP oxidoreductase, not only fails to utilize MOP as a sole carbon source, but also was inhibited in its growth by MOP and AGR. In contrast, the growth of mutants with insertions in other tested moc genes was not inhibited by either opine. Growth of strains NT1 or UIA5, a derivative of C58 that lacks pAtC58, was not inhibited by MOP, but growth of NT1 or UIA5 harboring pRE10, which codes for the MOP transport system, was inhibited by the opine. When a clone expressing mocC was introduced, the growth of strain NT1(pRE10) was not inhibited by MOP, although UIA5(pRE10) was still weakly inhibited. In strain NT1(pRE10, mocC), santhopine (SOP), produced by the oxidation of MOP by MocC, was further degraded by functions encoded by pAtC58. These results suggest that MOP and, to a lesser extent, SOP are inhibitory when accumulated intracellularly. The growth of NT1(pRE10), as measured by turbidity and viable cell counts, ceased upon the addition of MOP but restarted in a few hours. Regrowth was partly the result of the outgrowth of spontaneous MOP-resistant mutants and partly the adaptation of cells to MOP in the medium. Chrysopine, isochrysopine, and analogs of MOP in which the glutamine residue is substituted with other amino acids were barely taken up by NT1(pRE10) and were not inhibitory to growth of the strain. Sugar analogs of MOP were inhibitory, and those containing sugars in the D form were more inhibitory than those containing sugars in the L form. MOP analogs containing hexose sugars were more inhibitory than those containing sugars with three, four, or five carbon atoms. Mutants of NT1(pRE10) that are resistant to MOP arose in the zone of growth inhibition. Genetic and physiological analyses indicate that the mutations are located on pRE10 and abolish uptake of the opine.

scholarly journals KPC Beta-Lactamases Are Permissive to Insertions and Deletions Conferring Substrate Spectrum Modifications and Resistance to Ceftazidime-Avibactam

2020 ◽  
Vol 64 (12) ◽  
Author(s):  
Claire Amaris Hobson ◽  
Stéphane Bonacorsi ◽  
Hervé Jacquier ◽  
Alaksh Choudhury ◽  
Mélanie Magnan ◽  
...  
Keyword(s):  
Amino Acids ◽  
Klebsiella Pneumoniae ◽  
Active Site ◽  
Beta Lactamase ◽  
Content Type ◽  
Beta Lactamases ◽  
Extended Spectrum Beta Lactamase ◽  
Insertions And Deletions ◽  
Resistant Mutants ◽  
Substrate Spectrum

ABSTRACT To explore the mutational possibilities of insertions and deletions (indels) in the Klebsiella pneumoniae carbapenemase (KPC) beta-lactamase, we selected for ceftazidime-avibactam-resistant mutants. Of 96 screened mutants, we obtained 19 indels (2 to 15 amino acids), all located in the loops surrounding the active site. Three antibiotic susceptibility phenotypes emerged: an extended-spectrum-beta-lactamase-like phenotype, an activity restricted to ceftazidime, and a carbapenem-susceptible KPC-like phenotype. Tolerance for indels reflects the evolvability of KPC beta-lactamase, which could challenge the therapeutic management of patients.

A General Method for Selection of α-Acetolactate Decarboxylase-Deficient Lactococcus lactis Mutants To Improve Diacetyl Formation

1999 ◽  
Vol 65 (3) ◽  
pp. 1202-1206 ◽  
Author(s):  
Mirjana Curic ◽  
Birgitte Stuer-Lauridsen ◽  
Pierre Renault ◽  
Dan Nilsson
Keyword(s):  
Amino Acids ◽  
Lactococcus Lactis ◽  
Genetically Modified Organisms ◽  
Defined Medium ◽  
Isoleucine Leucine ◽  
Genes Encoding ◽  
Resistant Mutants ◽  
Branched Chain ◽  
Selection Of

ABSTRACT The enzyme acetolactate decarboxylase (Ald) plays a key role in the regulation of the α-acetolactate pool in both pyruvate catabolism and the biosynthesis of the branched-chain amino acids, isoleucine, leucine, and valine (ILV). This dual role of Ald, due to allosteric activation by leucine, was used as a strategy for the isolation of Ald-deficient mutants of Lactococcus lactis subsp.lactis biovar diacetylactis. Such mutants can be selected as leucine-resistant mutants in ILV- or IV-prototrophic strains. Most dairy lactococcus strains are auxotrophic for the three amino acids. Therefore, the plasmid pMC004 containing the ilv genes (encoding the enzymes involved in the biosynthesis of IV) of L. lactis NCDO2118 was constructed. Introduction of pMC004 into ILV-auxotrophic dairy strains resulted in an isoleucine-prototrophic phenotype. By plating the strains on a chemically defined medium supplemented with leucine but not valine and isoleucine, spontaneous leucine-resistant mutants were obtained. These mutants were screened by Western blotting with Ald-specific antibodies for the presence of Ald. Selected mutants lacking Ald were subsequently cured of pMC004. Except for a defect in the expression of Ald, the resulting strain, MC010, was identical to the wild-type strain, as shown by Southern blotting and DNA fingerprinting. The mutation resulting in the lack of Ald in MC010 occurred spontaneously, and the strain does not contain foreign DNA; thus, it can be regarded as food grade. Nevertheless, its application in dairy products depends on the regulation of genetically modified organisms. These results establish a strategy to select spontaneous Ald-deficient mutants from transformable L. lactis strains.

scholarly journals Construction and Characterization of Mutations at Codon 751 of the Escherichia coli gyrB Gene That Confer Resistance to the Antimicrobial Peptide Microcin B17 and Alter the Activity of DNA Gyrase

2001 ◽  
Vol 183 (6) ◽  
pp. 2137-2140 ◽  
Author(s):  
Francisco J. del Castillo ◽  
Ignacio del Castillo ◽  
Felipe Moreno
Keyword(s):  
Escherichia Coli ◽  
Amino Acids ◽  
Dna Gyrase ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Peptide Antibiotic ◽  
Resistant Mutants ◽  
Different Levels ◽  
Microcin B17

ABSTRACT Microcin B17 is a peptide antibiotic that inhibits DNA replication in Escherichia coli by targeting DNA gyrase. Previously, two independently isolated microcin B17-resistant mutants were shown to harbor the same gyrB point mutation that results in the replacement of tryptophan 751 by arginine in the GyrB polypeptide. We used site-directed mutagenesis to construct mutants in which tryptophan 751 was deleted or replaced by other amino acids. These mutants exhibit altered DNA gyrase activity and different levels of resistance to microcin B17.

Homochirality as the Signature of Extra-Terrestrial Life

1997 ◽  
Vol 161 ◽  
pp. 505-510
Author(s):  
Alexandra J. MacDermott ◽  
Laurence D. Barron ◽  
Andrè Brack ◽  
Thomas Buhse ◽  
John R. Cronin ◽  
...  
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Optical Rotation ◽  
Physical Origin ◽  
Natural Choice ◽  
Rosetta Mission ◽  
Terrestrial Life ◽  
Subsurface Layers ◽  
Solar System Bodies ◽  
Origin Of Homochirality

AbstractThe most characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. We therefore suggest that a search for extra-terrestrial life can be approached as a Search for Extra- Terrestrial Homochirality (SETH). The natural choice for a SETH instrument is optical rotation, and we describe a novel miniaturized space polarimeter, called the SETH Cigar, which could be used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. We believe that homochirality may be found in the subsurface layers on Mars as a relic of extinct life, and on other solar system bodies as a sign of advanced pre-biotic chemistry. We discuss the chiral GC-MS planned for the Roland lander of the Rosetta mission to a comet and conclude with theories of the physical origin of homochirality.

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